The common way of applying pesticides both outdoors in the field and indoors, for example in greenhouses and warehouses, is to spray the pesticide. These sprays are formulated for the particular application, and these formualations are prepared from a pesticide concentrate which is usually diluted with water or solvent prior to spraying. These pesticide concentrates may be 100% active ingredient, liquid or powder, or they can be solutions containing active pesticide from 20 to 95% in solvents, or they may be emulsifiable concentrates containing various percentages of active ingredient, or they may also be wettable powders. These concentrates are subsequently diluted with water and sometimes with other solvents and thus sprayed on to the plants or fields.
This spraying method has a number of drawbacks that make it undesirable. For one thing, spray particles settle on horizontal surfaces and leave unsightly residue. Furthermore, there is always a possibility of accumulating harmful chemical concentrations. The primary drawback of ordinary spraying, however, is that it is relatively inefficient and thus costly. This is because of the relatively large particle size of the spray drops. For example, a pesticidal particle of only five microns in size is adequate to kill an insect. Spraying produces particles of over 125 microns in size. Thus if we are able to get smaller particles they would be more efficient.
Aerosol sprays, which generally give finer particle size, are known for dispersing pesticides. They have, however, certain drawbacks. Aerosols are generally based on pressurized systems wherein a liquified gas is used to propel the pesticide into the atmosphere. These liquified gases are usually costly and also present handling problems. Furthermore, since the formulations must remain confined in a container under pressure until it is expanded there are certain safety risks.
One relatively new development in the application of pesticides is the concept of fogging. This is accomplished with an apparatus called a fogger which contains a tank for holding pesticide solutions or dispersions which are drawn into another section of the apparatus and flash evaporated by being heated with a very hot blast of air and forced through a nozzle. The hot air burns or consumes the solvents and spreads a thin dry mist and fog which covers a very large area.
Fogging offers a number of advantages over spraying one of which is smaller particle size. For example spraying can produce only about 225 million droplets from a quart of insecticide whereas fogging machines can break up insecticide to 14,000 billion effective particles per quart. This makes fogging approximately 65 times more efficient than spraying. Small particles not only make fogging more efficient than spraying but also more effective. Spray particles tend to settle on horizontal surfaces and with many sprays it is necessary for the pesticide to make contact with the insect. This means that if the pests, for example, in a warehouse or storage house are hidden under something like a carton or a box, the pesticide will never reach the pests. With fogging, however, because the particles are so small they remain airborne for longer periods of time and air currents carry them throughout the space of any indoor environment. The fog creeps under crates and crevices and makes contact with the pests whereever they may be. Another feature of pesticide fogs is that they leave no residue. Fogging produces particles of under 50 microns and while in the case of spraying you feel the wet spray, in fogging the fog is dry, and billions of micron size fog particles drift with air currents. The fogging also eliminates the danger of harmful chemical buildup. Some of the commercial foggers available are "London-Fog", "Dyna-Fog", and others. One key to the successful applications of a fog is the solvent or solvent system used to dissolve or disperse the pesticide concentrate for use in the foggers. The known solvents for fogging have been petroleum distillates, mixtures of ethylene glycol and methanol, mixtures of ethylene glycol monoethyl ether mixed with methanol and distilled water; a mixture of methylene dichloride and Risella oil. These solvent systems although useful have their limitations. Some of these are useful only with pesticide concentrate which are liquid, that is either solutions or emulsifiable concentrates, whereas others are only useful in formulations of wettable powders. None of them can be used as a universal solvent system for both liquid and solid pesticide concentrates.
Exterminators or applicators using fogging techniques have to either purchase ready made formulations for fogging specifically designed for each active ingredient, or they have to carry a stock of several different solvent systems for different types of concentrates if they wish to prepare their own fogging compositions.
Thus, there is a need for a single solvent system that can be offered to the end user for dissolving or dispersing both liquid and solid pesticide concentrates and yet giving excellent fogs.